
program chapter5_2
    implicit none
    real x, y
    x=1
    y=0
do 10, while(x .LT. 21)
    y=y+1/(x*(x+1))
    x=x+1
    print *, 'time=', x-1, 'this time y=', y
10 continue
    print *, 'sum=', y

end program

